Glacier meltwater contribution to river runoff in Western Mongolia

Study regions: Three river basins in western Mongolia (Khovd, Uvs, and Zavkhan). Study focus: Water resources in Mongolia, which have been poorly studied to date, are limited and unevenly distributed, with the contribution of glacier meltwater being unknown. We simulated the runoff in three river basins in western Mongolia that receive glacier meltwater. ERA5 reanalysis data were evaluated using observations at 28 meteorological stations, and then the glacier meltwater and river runoff were simulated using statistically downscaled ERA5 reanalysis data and three models: an energy-mass-balance model for glaciers, a land-surface process model for ice-free terrain, and a river runoff model to combine the runoff from the two terrains. The simulated runoffs are validated with observations at 34 hydrological stations. New hydrological insights for the region: The glacier meltwater contribution, which is first quantitatively evaluated, is substantial in the Khovd River basin, occurs only in some sub-basins of the Uvs Lake basin, and is negligible in the Zavkhan River basin. The glacier-free simulation indicates that, if glaciers were to disappear, river runoff would significantly decrease during the summer, with the peak flow shifting 1–2 months earlier compared to the present day. The glacier meltwater contribution to river runoff exhibits a nonlinear relationship with the glacier area contribution, which is much greater than that found in a previous study for Tien Shan, suggesting that shrinking ice mass would supply larger amounts of water. Analyses of correlation and extremes suggest that runoff from glacierized catchments responds differently than runoff from glacier-free terrains and thus would compensate for a water deficit caused by a warm and dry environment by supplying glacier meltwater, and vice versa. • Glacier meltwater contributions to river runoff are estimated in western Mongolia. • Shrinking glaciers supply additional water to river runoff in glacierized catchments. • Effects of precipitation and temperature on runoff depend on glacier contribution.